Extraction of zinc from its ores or products.



H. T. DURANT EXTRACTION 0F ZINC FROM ITS ORES OR PRODUCTS. APPLICATIONFILED MAY 4. 1914.

Patented Apr. 25, 1916;

2 SHEETS-SHEET I.

H. T. DURANT. EXTRACTION 0F ZINC FROM ITS ORES OR PRODUCTS.

APPLICATION FILED MAY 4, 1914.

Patented Apr. 25, 1916.

2 SHEETSSHEET 2.

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Nl l Ell STATES PATENT OWWMWEW HENRY THOMAS DURANT, OF LONDON, ENGLAND,ASSIGNOR TO THE METALS EXTRACTION CORPORATION LIMITED, OF LONDON,ENGLAND.

EXTRACTION 0F ZINC FROM ITS ORES OR PRODUCTS.

Specification of Letters Patent.

Patented Apr. 25, rare.

Application filed May 4, 1914. Serial No. 836,313.

To all whom it may concern Be it known that I, HENRY THOMAS DU- RANT, asubject of the King of England, residing at Finsbury House, Blomfield'Street, London, England, have invented certain new and usefulImprovements in the Extraction of Zinc from Its Or es or Products, ofwhich the following is a specification.

This invention is for improvements in or relating to the extraction ofzinc from its ores and concentrates or from complex ores or products,that is to say from all ores orv products whether natural or artificialwhich contain zinc with or without other metal values such as lead,copper, silver or gold.

This invention consists in improvements and modifications in theprocesses of the convert the zinc into oxid or sulfate or a mixture ofboth.

Throughout this specification the Word ore is used to denote any ore orother metalliferous product containing zinc. Where the ore contains zincmainly as oxid, carbonate, silicate, or sulfate, some other source ofsulfur is necessary to produce furnace gases, i. e. the S0 Ores may becrushed to the degree of fineness ultimately required and then ifnecessary roasted, or they may be coarsely crushed before roasting andif necessary further crushed after roasting. The ore after roasting ifnecessary is screened, so as to give a coarse or leachable and a fine ornonleachable product. Obviously the ore may be so fine that it containsno coarse or leachable product, in which case the leaching tanks are notused and the whole of it is treated in filter presses or equivalentapparatus as hereinafter described.

According to previous practice the ore containing zinc, having beenfirst roasted if necessary, was' suspended in water and broughtinto-intimate contact with a gas containing SO (such as roasting furnacegas) for the purpose of causing the zinc to go into solution asbisulfite, and this operation was generally carried out in an apparatusof the type described in United States Patent No. 999,213, or in asolution barrel or in a combination of these devices. When the ore orproduct requires roasting it has hitherto been necessary to roast thematerial in muflle furnaces in order to obtain the S0 in concentratedform.

One object of' this invention is tosimplify the method of solution.

Another object of this invention is to allow of the employment ofreverberatory furnaces which are very much simpler and commercially moreeconomical than mufile furnaces.

A third object of this invention is to provide a cyclic process in whichthe highest possible extraction of zinc can be readily obtained, whileif still of value the residues after the process treatment are producedin a suitable form for further treatment, whether smelting orconcentration, for recovery of those metal values other than the zincand some of the copper which goes into solution with the zinc.

According to this invention the process for the extraction of zinc fromits ores or products consists in introducing crushed material(previously roasted if necessary) into a filter press or leaching tankand leaching the material with a solution of sulfur-dioxid (S0 ashereinafter described.

A feature of this invention when roasting is -required consists inroasting the ore or product in a reverberatory furnace and passing. thefurnace gases into an absorpbeing classified as will be hereinafterexplained for the purpose of recovering its metal values.

A further feature of this invention when roasting is required consistsin roasting the ore or product so as to produce mainly sulfate of zinc,whereby the first runnings of solution obtained from the filter-press orleaching tank are rich in Zinc sulfate while the solutions subsequentlyleached ofi contain mainly Zinc sulfite.

Figure l is an elevation of a suitable plant for carrying out thepresent process. Fig. 2 is a diagrammatic view showing the "arious stepsof the present process.

The ore (or other material as a source of sulfur) is roasted in afurnace A so as to give of]? SO containing gases. This furnace may beeither a mufl'le, such as a Hasenclaver or Merton furnace, or may be areverberatory furnace. The ore or prodnot is roasted so as to obtain aslarge a percentage of' sulfate as possible. The furnace gases are passedinto and up an absorption tower B, and from the tank B the circuitsolution is delivered to the top of the tower, so that a solution of S0is produced therein and discharged at the bottom into the tank C whichacts as a storage. Preferably there is employed a cone tower asdescribed for example in our previous United States Patent No. 999213but the tower shown as B may be replaced by any other device forscrubbing a gas with a solution or water. The flue gases from which SO'has been removed wholly or in part escape through a chimney B of thetower B.

The coarse leachable product before men-.

tioned is treated with the S0 circuit solution in ordinary leachingtanks D and D in which the solution passes through under its ownpressure due to its static head.

To prevent caking of thematerial in the initial stages of the leachingit may be necessary either to use a small quantity of the circuitsolution hot or to agitate the coarse roasted ore or product with aboutits own weight of the circuit solution in a pulping tank F or the likebefore running into the leaching tank.

The leaching may be carried out in one tank until most of the Zinc isextracted; the partially treated material may then be transferred toanother tank, for further leaching, in this'way the zinc is extractedmore easily and thoroughly. This procedure "is, generally advisable, asthe transference from one tank to another breaks u the leaching channelsin the material. Af-

. ter treatment is finished the residues from I for other metal valuesleaching arewater washed and are then commercially zinc free and can betreated I they may contain.

The fine non-leachable product is pulped up with circuit solution in apulping tank F orthe like, and is pumped by a force pumpintoa filter,preferably a filter. press EJ y In pulping, enough solution is used 'togive aratio of solid'to liquid of about 1:1,

that isto'say, the pulp should be quite thick so'asfto preventsegregation and stratificathe solutions leached from the coarse mater1alare exactly comparable with those that leave the filter press it is onlynecessary to consider these latter. The first runnings of solution fromthe filter press are rich in Zinc sulfate, the amount of this solutionbeing about equal to the amount of circuit solution used for pulping upthe fine nonleachable product previous to pumping it into the filterpress. This sulfate solution is separately stored in the tank L. Thenext solution which runs from the filter press is poorer in zincthissolution is neuand 1s sepatral- 6. free from free acid) rately stored inthe tank K. Finally solution containing free acid will leave the filterpress; this solution is also separately stored in the tank J.

When it is shown by testing that the amount of free acid leaving thefilter press approximates to the amount entering, the charge of fines inthe filter press has finished its first treatment. The filter press maythen be discharged, and the partially treated material from the filterpress may, to make up for its decrease in volume, be pulped up with morepartially treated material and circuit solution and pumped back into thefilter press so as to again fill the press and make another completecharge. After this has been done more circuit solution is pumped in bythe washing pump until a test shows that the quantity of free acidleaving the filter press is about the same as that entering it.Thereupon the circuit solution is shut off and enough water is pumped into displace the remaining circuit solution and the completely extractedmaterial is discharged. As an alternative to this procedure, the presshaving been filled as first described, and the bulk of the Zinc havingbeen extracted by washing with the acid solution, as before described,the washing operations may be stopped and enough pulped up fines to fillup the press may be pumped in, after which washing can be continued asusual. In place of the filter press, other filters can be used such asvacuum filters of the drum or leaf type.

Sometimes practically all the soluble zinc is extracted during onefilter press treatment, that is'to say, having discharged the materialfrom the filter press, it is not necessary to put it back again forfurther treatdescribed is not necessary.

ment along with some more partly treated material, as described above,or to pump more pulpedup fines into the filter press, which as describedabove is analternative method to the same end. Exactly the same remarkapplies to the leaching of the coarse material in the leaching tanks; attimes practically all the soluble zinc is extracted in the firstleaching tank and therefore transference to the second tank aspreviously The residues from the filter press are treated for theirmetal values in the same way as the residues from leaching of the coarsematerial; these residues containing all the lead, silver, etc., and someof the copper as previously stated.

The solution of zinc runs. clear from the filter press or leachingtanks. In proportion as the roast has been a sulfate roast, the firstrunnings from the press are rich in zinc sulfate. After the firstrunning the zinc will form a comparatively dilute solution which will bemainly zinc sulfite. This solution from the filter press may contain say0.5% to 1% of zinc more than the average zinc contents of the circuitsolution.

If the solution contains only zinc sulfate no oxidation is necessary. Ifthe solution contains zi'nc sulfite it is subjected to an oxidizingprocess to convert the zinc into sulfate. This oxidation is necessarymainly for three reasons :(1) Because the solution sent back to the topof the absorption tower should be practically free from sulfites inorder that it may be capable of absorbing the maximum amount ofavailable SO (2) Because SO or sulfites would interfere with theprecipitation of copper by zinc dust or scrap iron. (3) Because zincsulfite in absence of free S0 will crystallize in the pipe lines.

Preferably the oxidation of thesolution is carried out in tanks M and Nto each of=which is connected at the bottom a centrifugal pump whichdischarges the solution back into the top of the tank while. atmosphericor compressed air is admitted into the inlet of the centrifugal pump. Bythese means the solution is brought into intimate contact with air in afinely divided state and zinc sulfite is changed into sulfate. Thesolution may then if necessary be treated for the precipitation ofcopper either by zinc dustor scrap iron. In the case where the zinc dustis used an apparatus 0 similar to that just described may be utilized,the zinc dust going around with the solution through the tank andcentrifugal pump. This procedure is mechanically similar to theoxidizing procedure but without the introduction of the air. Thesolution thus treated and containing zinc sulfate is split, that istosay. a portion is removed and evaporated for the precipitation of asmuch zinc as is necessary to maintain the equilibrium of the circuit.The remainder of the circuit solution is made up to normal quantity bythe final water-washings used in the leaching tank and (or) filterpress. The circuit solution is then returned to the absorption tower.Thus all solution removed for precipitation (evaporation) of the zincvalues is first oxidized (if it contains muchsulfite) and is thentreated with zinc dust as described or by other means for the removal ofcopper, and this solution removed for precipitation of zinc valuesprimarily consists of the rich sulfate solution with enough circuitsolution added to maintain the average'zinc contents of the solution andthereby daily to remove as much zinc as is daily added. Similarly allthe remainder of'the solution from filter presses or leaching tanks isoxidized to convert the greater part of the sulfites into sulfatesbefore this solution is again sent to the absorption towers to absorbmore S0 The precipitation of the solution can be done by any convenientmethod of evaporation, for example in a reverberatory furnace H, firstto form zinc sulfate, then anhydrous zinc sulfate and then zinc oxid bycalcination.

What I claim as my invention and desire to secure by Letters Patentis 1. The herein-described process for the extraction of zinc from itsores which consists in roasting the ore so as to convert most of thezinc into sulfate, passing the furnace gases through circuit solutionfairly free from sulfites so as to form a solution of sulfur dioxid, andsubjecting the roasted ore simultaneously to leaching with a solution ofsulfur dioxid and'to pressure filtration so as to leach out the zincsulfate from 5' the ore and dissolve out the remaining zinc in the formof sulfates and sulfites.

2. The herein described process for the extraction of zinc from its oreswhich consists in roasting the ore, passing the furnace gases throughcircuit solution containing metallic sulfates but fairly free fromsulfites so as to produce a solution of sulfur dioxid, and leaching theore with the said solution of sulfur dioxid.

3. The herein described process for the extraction of zinc from its oreswhich consists in roasting the ore so as to produce mainly sulfate ofzinc, passing the furnace gases through circuit solution containingmetallic sulfates but fairly free from sulfites so as to produce-asolution ofsulfur dioxid, and leaching the ore with the said solution ofsulfur dioxid whereby the first runnings from the leached ore are richin extraction of zinc from its ores which con "sists in roasting the oreso as to produce mainly sulfate of zinc; passing the furnace gasesthrough circuit solution containing metallic sulfates but fairly freefrom sulfites so as to produce a solution of sulfur dioxid, and leachingthe ore with the said solution of sulfur dioxid to produce firstsolutions rich in sulfate and subsequently solutions containing metallicsulfites, and oxidizing the sulfite-containing solutions so as toconvert the sulfites into sulfates.

The herein described process for the extraction of zinc from its oreswhich consists in roasting the ore so as to convert most of the zincinto sulfate, passing the furnace gases through circuit solution fairlyfree from sulfites so as to form a solution of sulfur dioxid, subjectingthe roasted ore simultaneously to leaching with a solution of sulfurdioxid and to pressure filtration so as to leach out the zinc sulfatefrom the ore and dissolve out the remaining zinc in the form of sulfatesand sulfites, oxidizing the sulfite containing solution so as to convertthe sulfites into sulfates, splitting off a portion of the whole amountof the solution of zinc sulfate thus obtained for the extraction of thezinc therefrom and making up the circuit solution from the remainder ofthe sulfate solutions together with the requisite amount of water toreplace the solution split off.

6. The herein described process for the extraction of Zinc from its oreswhich con sists in roasting the ore so as to convert mostof the zincinto sulfate, passing the furnace gases through circuit solution fairlyfree from sulfites so as to form a solution of sulfur dioxid, subjectingthe roasted ore simultaneously to leaching with a solution of sulfurdioxid and to pressure filtration so as to leach out the zinc sulfatefrom the ore and dissolve out the remaining zinc in the form of sulfatesand sulfites, oxidizing the sulfite containing solution by means of airso as to convert the sulfites into sulfates, splitting off a portion ofthe whole amount of the solution of zinc sulfate thus obtained,

precipitating the copper from the split ofi portion of the solution ofzinc sulfate, and evaporating the purified solution of zinc sulfate soas first to form zinc sulfate then anhydrous zinc sulfate and then zinc,oxid by calcination.

7. The herein described process for the extraction of zinc from its oreswhich consists in roasting the ore so as to convert most of the zinclnto sulfate, passing the furnace gases through circuit solution fairlyfree from sulfites so as to form a solution of sulfur dioxid, subjectingthe roasted ore simultaneously to leaching'with a solution of sulfurdioxid and to pressure filtration so as to leach out the zinc sulfatefrom the ore and dissolve out the remaining zinc in the form of sulfatesand sulfites, oxidizing the sulfite containing solution by means of airso as to convert the sulfites into sulfates, splitting off a portion ofthe whole amount of the solution of zinc sulfate thus obtained,precipitating the copper from the split off portion of the solution ofzinc sulfate, and evaporating the purified solution of zinc sulfate soas first to form zinc sulfate then anhydrous zinc sulfate and then zincoxid by calcination and making up the circuit solution from theremainder of the sulfate solution, together with the requisite amount ofwater to replace the solution split off.

8. The herein described process for the extraction of zinc from its oreswhich consists in first roasting the ore so as to obtain most of themetals in the form of sulfate, separating the product thus obtained intoa coarse leachable material and a fine nonleachable material, leachingthe coarse material with a solution of sulfur dioxid so as to producefirst solutions of zinc sulfate and then solutions of zinc sulfite andsulfate, forming a pulp of the fine non-leachable material, subjectingthe said pulp simultaneously to leaching with a solution of sulfurdioxid and to pressure filtration so as to produce first solutions'ofzinc sulfate and then solutions of zinc sulfate and zinc sulfite,utilizing part of the zinc-containing solutions for the extraction ofthe zinc therefrom and the remainder of the said solutions for thecircuit liquor, and treating the residues from the coarse and finematerials for-the recovery of any metals contained therein.

9. The herein described process for the extraction of zinc from its oreswhich consists in first roasting the ore so as to obtain most of themetals in the form of sulfate, separating the product thus obtained intoa coarse leachable material and a fine nonleachable material, leachingthe coarse material with a solution of sulfur dioxid so as to producefirst solutions of zinc sulfate and then solutions of zinc sulfite andsulfate, forming a pulp of the fine non-leachable material, subjectingthe said pulp simultaneously to leaching with a solution of sulfurdioxid and to pressure filtration so as to produce first solutions ofzinc sulfate and then solutions of zinc sulfate and zinc sulfite,collecting the first runnings rich in zinc sulfate obtained from boththe coarse leachable material and the fine non-leachable materialseparately from the subsequent solutions leached from the ore poor insulfate and containing sulfite, oxidizing the sulfite-containingsolutions so as to convert the sulfites into sulfates, splitting off aportion of the sulfite-containing solutions and removing the coppertherefrom by precipitation with zinc, evaporating the purified solutionof zinc sulfate so as to finally produce zinc oxid, and returning theremainder of o the sulfate solution, Without removing any copper thatmay be contained therein, to the main circuit for the absorption ofsulfur dioxid.

10. The herein described process for the extraction of zinc from itsores which consists in first roasting the ore so as to obtain most ofthe metals in the form of sulfate, separating the product thus obtainedinto a coarse leachable material and a fine nonleachable material,leaching the coarse material With a solution of sulfur dioxid so as toproduce first solutions of zinc sulfate and then solutions of zincsulfite and sulfate, forming a pulp of the fine non-leachable material,subjecting the said pulp simultaneously to leaching with a solution ofsulfur dioxid and to pressure filtration so as to produce firstsolutions of zinc sulfate and then solutions of zinc sulfate and zincsulfite, collecting the first runnings rich in zinc sulfate obtainedfrom both the coarse leachable material and the fine non-leachablematerial separately from the subsequent solutions leached from the orepoor in sulfate and containing sulfite, oxidizing the sulfite-containingsolutions so asvto convert the 'sulfites into sulfates splitting ofi aportion of the sulfite-containing solutions and removing the coppertherefrom by precipitation with scrap iron, evaporating the purifiedsolution of zinc sulfate so as to finally produce zinc oxid, andreturning the remainder of the sulfate solution, without removing anycopper that may be contained therein, to the main circuit for theabsorption of sulfur dioxid.

11. The herein described apparatus for carrying out a continuous processfor the extraction of zinc from its ores comprising a furnace whereinthe ore is roasted in free contact With air, a tower into which thecircuit solution is delivered andthrough which the furnace gases arepassed so as to produce a solution of sulfur diOXid, storage tanks forthe solution of sulfur dioxid leaving the tower, tanks in which thecoarse leachable ore is treated with the leaching solution, tanks forpulping up the fine non-leachable material, filter presses into whichthe fine material is introduced and'leached, tanks for collectingseparately the solutions rich in sulfate, the neutral solutions poorerin zinc and the acid solutions containing zinc sulfite, tanks providedwith centrifugal pumps for oxidizing the sulfite solutions and for theprecipitation of copper, tanks for storing the purified sulfatesolutions, and a reverberatory furnace for evaporation of the zincsulfate solution and recovery of the zinc therefrom in the form of zincoxid.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing witnesses.

I HENRY THOMAS DURANT. Witnesses:

VICTOR ARMSTRONG WATERS, T OMAS HENRY HOPPE.

